For protecting shaped articles against corrosion a plurality of materials is employed. Shaped articles such as man hole covers, underground tanks, pipes, lines and the like are often made of metal, metal compositions or alloys and such shaped articles are subject to corrosion since they are in contact with salts, moisture, water and other corrosive components. Corrosion is obviously not preferred since it is detrimental to strength and must therefore be prevented or inhibited to extend the life cycle of the shaped article as much as possible.
Obviously, materials for preventing corrosion, in particular long-term corrosion, must have a long-term chemical, physical, mechanical and thermal stability. Moreover, as is well known in the art, the application of such materials is often a laborious, time-consuming and expensive process. The materials must further have a good adhesion on metals and other materials like polyethylene and polypropylene. Another requirement is that they have a very low permeability for water, salts, moisture, and the like.
Several materials for inhibiting or preventing corrosion are known in the art. Examples of such materials are bitumen and synthetic, thermosetting resins, e.g. epoxy resins and polyurethane resins. These materials have the disadvantage that a hard coating or seal is produced which can easily split or tear under the influence of for example mechanical stress. Another disadvantage of these materials is that volatile solvents are required when such materials are applied. After application of these materials, the solvents evaporate thereby leading to the formation of a micro-porous seal or coating which is at least permeably for corrosive substances such as salts, water and moisture. Nor are the solvents friendly to the environment.
Bitumen are also permeable for water and do generally not meet the requirements laid down by the KIWA (“Keuringsinstituut voor Waterleidingartikelen”; Dutch Inspection institute for Water Supply Articles). Moreover, bitumen have in general a glass transition temperature of more than about 10° C. As a consequence, removal of bitumen is difficult under high temperature conditions, e.g. the summer, and formation of cracks can easily occur during low temperature conditions, e.g. the winter.
Synthetic, thermosetting resins are also easily split or torn as a result of mechanical stress. Moreover, they are not easily removed from the shaped article and easy removal is important when repairs have to be carried out to the shaped article or when the level of protection provided by the thermosetting resin needs to be checked. In addition, cleaning of the shaped article is also difficult which is required when a new seal or coating is applied so that complex and laborious cleaning techniques such as sand blasting have to be employed for cleaning the shaped article to a sufficient extent It is obvious to the person skilled in the art that if the shaped article is a gas or oil line or pipe line of several hundreds of miles long, replacing or repairing a seal or coating made of synthetic, thermosetting resins is a time-consuming and expensive operation. Finally, applying a seal or coating based on synthetic, thermosetting resins in it self is difficult and laborious.
U.S. Pat. No. 5,398,044 discloses a composition having improved properties when compared with the materials discussed above. This composition comprises an apolar, non-thermosetting fluid polymer, e.g. polyisobutene, having a glass transition temperature lower than −20° C. and a surface tension of less than 40 mN/m at temperature above its glass transition temperature, and a filler material. The composition may contain an anti-oxidant such as 2,6-di-t-butyl-4-methylphenol (BHt). The composition can be used in combination with a shrink sleeve, a tape, a belt, a mat or a tape having an open cell structure. However, the composition according to U.S. Pat. No. 5,898,044 has certain disadvantages. For example, if the composition contains 2,6-di-t-butyl-4-methylphenol as the anti-oxidant, the present inventors have found that the anti-oxidant leaches out of the composition thereby deteriorating the protecting properties of the composition due to oxidative degradation of the non-thermosetting fluid polymer. This has the disadvantageous effect that the adhesive strength of the composition deteriorates over time when applied to a shaped article. Consequently, this sealing system have a reduced life cycle and requires earlier repair or replacement than desired. Since the sealing system is required to have a long life cycle, i.e. in general more than 50 years, and the application thereof is expensive and laborious, it is obvious to the person skilled in the art that such a sealing system needs improvement. Therefore, the inventors have investigated this technical problem and discovered that the decrease of adhesive strength is caused by leaching out of 2,6-di-t-butyl-4-methylphenol.
WO 99/56055 discloses a method for protecting a metal pipe against corrosion by applying a film to the metal pipe. The film comprises an outer layer, an intermediate layer and an inner layer. The outer layer is preferably made from a polymer, in particular high density polyethylene. The intermediate layer is preferably made of a metal in particular aluminium. The inner layer comprises preferably an adhesive or mastic. The film must be applied by employing heat. As is obvious to the person skilled in the art, this method is laborious and time-consuming and inferior to the methods disclosed in U.S. Pat. No. 5,898,044.
WO 99/48997 discloses a composition comprising an organic material that is subjective to oxidative, thermal or light-induced degradation and two or more anti-oxidants, wherein the organic material may be selected from a wide range, of materials including polyisobutene. According to page 44 of WO 99/45997, the compositions may be used in an extreme wide variety of applications, e.g. in lubricating oils, hydraulic fluids and in metal-working fluids. However, WO 99/48997 does not disclose that the composition can be used for protecting a shaped article against corrosion.
EP A 1.086.963 discloses an ethylene copolymer composition that can be used as a gasket, e.g. a corrosion-resistant pipe joint. Obviously, such a gasket is placed between two pipe ends when the pipes are joined together to prefer leakage.